1. Technical Field
The present invention relates to a packet transfer device and a power supply control method for a quality of service (QoS) control circuit, and more particularly to a packet transfer device that realizes a QoS control function used in a communication device such as a router or a switch and an energy saving control system thereof, and a power supply control method for the QoS control circuit.
2. Related Art
Packet transfer devices such as a router or a switch currently used in packet communication have a large number of functions. Among those functions, a QoS control function (scheduling function, policer function, buffering function, etc.) is implemented by hardware with high percentage. A QoS control is a technique for designating and controlling transfer characteristics (delay priority or loss priority) according to identification information on a packet to be transferred (for example, identifiers of a destination or source address, or an upper layer protocol, identifiers of VPN No. or VLAN, etc.). Among those QoS control, the scheduling function (or shaping function) is provided at an output port from a device to a line, and most effective as a technique making some distinction in the transfer characteristics.
A variety of systems have been known for the scheduling function. For example, there is “priority queuing system (hereinafter referred to as “PQ system”). In the PQ system, plural queues are provided for the respective priorities, and each packet is loaded into a queue corresponding to the delay priority of the packet. The loaded packets are extracted from the queues in a descending order of the priority by the scheduler and transferred. The packets loaded into the queues lower in the priority are transferred after all of the packets loaded into the queues higher in priority have been transferred. As a result, it is ensured that the packets loaded into the queues higher in the priority are transferred with a smaller delay time than that of the packets loaded into the queues lower in the priority. With this effect, for example, it can be ensured that a delay time value of voice packets is suppressed to a given time or shorter. Also, as another scheduling system, there is “weighted fair queuing system (hereinafter referred to as “WFQ system”). The WFQ system controls bandwidth values which are transferred from plural queues on the basis of predetermined weight values. Even when the packets of the queues higher in the priority are continuous, the WFQ system is effective to a case in which transfer of the packets of the queues lower in the priority is ensured according to the weight value of the WFQ, and a given service level is to be ensured for each application. Up to now, plural other scheduling systems, and systems combining those systems together have been proposed.
In this way, the scheduling function is realized by the function of classifying and accumulating the packets into the plural queues according to the identification information of the packets, and the function of extracting the packets from the plural queues according to a specific algorithm. Those scheduling functions are selectively used according to a status of the packets (traffic) to be transferred on a network, or the type of service to be provided.
On the other hand, JP-A-2001-345861 discloses a technique by which the packets input from a local area network are monitored to dynamically change (decrease) the number of queues upon sensing an increase in the traffic, thereby preventing an excessive traffic from flowing. The queues are decreased to intentionally discard the packets.
Also, JP-A-2003-283552 (reference numerals in this paragraph are disclosed in JP-A-2003-283552) discloses the provision of a monitor unit 11 that periodically and automatically acquires traffic information for specifying characteristics of an input traffic in a QoS control router 2 at given time intervals. JP-A-2003-283552 also discloses the provision of a QoS control system selector 12 that selects an optimum QoS control system in the QoS control router 2, on the basis of a traffic volume specified from the traffic information acquired from the monitor unit 11, and externally controls a router setting device 4 so that a required QoS control based on the QoS control system for this selection is executed in the corresponding QoS control router 2.
Also, JP-A-2002-281066 discloses a queue assignment system and a queue assignment method for a packet switch, and more particularly a queue assignment system and a queue assignment method for a packet switch, which reduce the degradation of a transmission quality attributable to the concentration of traffic on one queue.